Archived

Avalanche Forecast

Mar 4th, 2017–Mar 5th, 2017

Alpine

3: Considerable

The avalanche danger rating in the alpine will be considerable

Treeline

3: Considerable

The avalanche danger rating at treeline will be considerable

Below Treeline

2: Moderate

The avalanche danger rating below treeline will be moderate

Alpine

3: Considerable

The avalanche danger rating in the alpine will be considerable

Treeline

2: Moderate

The avalanche danger rating at treeline will be moderate

Below Treeline

2: Moderate

The avalanche danger rating below treeline will be moderate

Alpine

3: Considerable

The avalanche danger rating in the alpine will be considerable

Treeline

2: Moderate

The avalanche danger rating at treeline will be moderate

Below Treeline

1: Low

The avalanche danger rating below treeline will be low

Regions: Lizard-Flathead.

A week of heavy snowfall and strong winds have left large storm slabs primed for human triggering. Avoid overhead hazards and stick to mellow terrain.

Confidence

High - Due to the number and quality of field observations

Weather Forecast

SUNDAY: Afternoon flurries with 5-10 cm of new snow, moderate southwest winds, alpine temperatures around -7 C.MONDAY: Cloudy with isolated flurries and trace accumulations, strong southwest winds, alpine temperatures around -10 C.TUESDAY: Cloudy with light flurries picking up in the afternoon, strong southwest winds, alpine temperatures around -10 C.

Avalanche Summary

A widespread natural avalanche cycle occurred on Friday night, with many size 2-3 cornice triggered avalanches on north and east aspects. Explosive avalanche control on Saturday produced size 2 storm slabs and ski cutting produced size 1-1.5 avalanches on wind-loaded features. Natural activity is expected to taper off, but storm slabs will remain primed for human triggering.

Snowpack Summary

Another 20 cm of snow fell on Friday, bringing the three day storm total to roughly 80 cm and the weekly total to almost 150 cm. Strong southwest winds have extensively redistributed the snow and formed large brittle cornices. The new snow is rapidly settling into a denser slab which sits over a variety of old surfaces including surface hoar, facets, stiff wind slabs, sun crusts, and a rain crust below 1900 m. Isolated basal weaknesses may still exist in shallow snowpack areas and appear to isolated to north-northeast aspects in the alpine.

Avalanche Problems

Storm Slabs

Storm slabs are primed for rider triggering, especially on leeward slopes and behind terrain features that are wind loaded.

Avoid leeward slopes as a thicker, reactive slabs will likely exist.The new snow will require several days to settle and stabilize.Use conservative route selection, choose moderate angled and supported terrain with low consequence.

Aspects: All aspects.

Elevations: All elevations.

Likelihood: Likely

Expected Size: 1 - 3

Cornices

Always look up and avoid exposure to overhead cornices.

Do not travel on slopes that are exposed to cornices overhead.Stay well back from cornices.

Aspects: North, North East, East.

Elevations: Alpine.

Likelihood: Likely

Expected Size: 1 - 2

Deep Persistent Slabs

There have been two natural deep persistent slab releases in the past week. Both of these avalanches were on northeast aspects in the alpine, and released to size 3 or larger.

Be aware of the potential for large, deep avalanches.If triggered the storm slabs may step down to deeper layers resulting in large avalanches.Pay attention to overhead hazards like cornices which could easily trigger deep slabs.

Aspects: North, North East, East, South East.

Elevations: Alpine, Treeline.

Likelihood: Unlikely

Expected Size: 2 - 4